In an ink-jet recording system, fine droplets of a recording liquid such as an ink are flown by various working principles to apply them to an ink jet recording medium such as paper, thereby making a record of images and/or characters. The ink jet recording medium used in this system has such features that recording can be conducted at high speed and with a low noise, color images can be formed with ease, recording patterns are very flexible, and development is unnecessary, and is hence further developed for output parts in information instruments such as copying machines, word processors, facsimiles and plotters in addition to printers, so that it is rapidly widespread.
In recent years, high-performance digital cameras, digital video cameras and scanners have begun to be provided cheaply, and printers using the ink jet recording system have come to be extremely favorably used for output of image information obtained from such instruments with the spread of personal computers.
Under such a background, there is a demand for simply and easily outputting images comparable in quality with silver salt photographs and multi-color prints of a plate making system using an ink jet recording system. In order to meet such a demand, improvements in structures and recording systems of printers themselves, such as speeding up and higher definition of recording, and full-coloring of images, have been made.
On the other hand, with respect to ink jet recording media used in the ink jet recording system, a wide variety of recording media has heretofore been proposed. An ink jet recording medium capable of forming an image comparable with a silver salt photograph requires formation of an image excellent in coloring of dyes and high in surface glossiness and resolution. In Japanese Patent Application Laid-Open No. H07-232475, an alumina hydrate is used as a component of an ink receiving layer of such an ink jet recoding medium.
Moreover, ink jet recording media have recently been required to have good preservability of images recorded as well. It has thus been proposed to improve the preservability of the recorded image by incorporating an image fading preventing agent for improving light fastness and gas fastness.
Japanese Patent Publication No. H06-030951 discloses a recording sheet containing a particular cationic compound as a method for improving the preservability of an image against light and gasses in the air. Japanese Patent Application Laid-Open No. H03-013376, Japanese Patent Publication No. H04-034512, Japanese Patent Application Laid-Open No. H11-245504 and Japanese Patent Application Laid-Open No. 2001-121812 respectively disclose recording sheets containing a hindered amine compound as a light fastness improver.
On the other hand, Japanese Patent Application Laid-Open No. 2000-177241 discloses a recording medium containing a phosphite compound as an image fading preventing agent. Japanese Patent Application Laid-Open No. 2006-123316 and Japanese Patent Application Laid-Open No. 2004-188667 investigate a recording medium containing a pentavalent phosphate compound and a recording medium containing a pentavalent phosphoric acid derivative, respectively, for the purpose of more improving the image fading preventing property. The recording media containing these pentavalent phosphates are said to be excellent in image preservability compared with the recording media containing the phosphite compound, hindered amine or sulfur compound.
The ink jet recording media described in Japanese Patent Publication No. H06-030951, Japanese Patent Application Laid-Open No. H03-013376, Japanese Patent Publication No. H04-034512, Japanese Patent Application Laid-Open No. H11-245504 and Japanese Patent Application Laid-Open No. 2001-121812 exhibit an effect to some extent on gas fastness and light fastness. However, the gas fastness and light fastness do not reach a level satisfactory to practical use in some cases according to the layer structures or components thereof.
Japanese Patent Application Laid-Open No. 2000-177241, Japanese Patent Application Laid-Open No. 2006-123316 and Japanese Patent Application Laid-Open No. 2004-188667 teach that the effect to prevent image fading is achieved by using the phosphite or pentavalent phosphate compound as an image fading preventing agent. The recording media described in these documents can achieve the improvement in weatherability to some extent by the use of the image fading preventing agent. In order to achieve sufficient image preservability, however, it is necessary to add the image fading preventing agent in a great amount. As a result, image characteristics such as image clearness and ink absorbency are deteriorated.
On the other hand, a dispersion with an inorganic pigment dispersed in a solvent is used for various applications. However, the dispersibility of the inorganic pigment in the solvent is deteriorated according to the materials used and the distribution of the inorganic pigment in a product formed with this dispersion is thus deteriorated to lower the characteristics of the product in some cases. In particular, when a coating liquid for an ink receiving layer of an ink jet recording medium is used as the dispersion, this tendency markedly appears according to materials used in the coating liquid. More specifically, the dispersibility of the inorganic pigment in the coating liquid is deteriorated and the distribution of the inorganic pigment in the ink receiving layer formed by applying and drying this coating liquid becomes uneven to lower the image characteristics of the resulting ink jet recording medium in some cases.
Here, it is considered that a coating liquid for an ink receiving layer which contains an image fading preventing agent such as the phosphite or pentavalent phosphate compound in a solvent and an inorganic pigment is used as the dispersion to produce an ink jet recording medium. In this case, however, the image fading preventing agent is often insoluble in water, and so the agent cannot be added into an aqueous coating liquid, or the dispersibility of the inorganic pigment is deteriorated if the agent can be added, and image characteristics such as image clearness are deteriorated by the unevenness of distribution of the inorganic pigment in the ink receiving layer.